It is known to provide a digital wireless apparatus which applies distortion compensation to a baseband modulated signal in a distortion compensator, converts the distortion-compensated signal into an analog signal by a D/A converter using a sampling clock of a first frequency, and amplifies the signal by a power amplifier PA for transmission, wherein a portion of the transmitted signal is fed back and demodulated, and the distortion component occurring in the PA is detected to calculate a distortion compensating coefficient for canceling out the distortion. In this digital wireless apparatus, the feedback signal is converted by a frequency converter into an intermediate frequency IF signal, the IF signal is undersampled by an A/D converter using a sampling clock of a second frequency, the output signal of the A/D converter is demodulated through digital quadrature demodulation into a first quadrature-demodulated signal, and a second quadrature-demodulated signal for distortion component detection is extracted from the first quadrature-demodulated signal by using an LPF. In this digital wireless apparatus, a carrier wave to an analog quadrature modulator and an oscillator frequency signal to the frequency converter, as well as the sampling clocks of the first and second frequencies, are generated using a common reference oscillator source. The digital wireless apparatus is equipped with a digital FIR filter which removes a frequency component at one-half the second frequency from the first quadrature-demodulated signal.
It is also known to provide a distortion compensating apparatus which applies distortion compensation to an input signal by using a distortion compensating coefficient and supplies the distortion-compensated signal to a distortion device, and which computes a distortion compensating coefficient, based on the input signal before the distortion compensation and on a feedback signal fed back from the output side of the distortion device, and stores the thus computed distortion compensating coefficient by associating it with the input signal. This distortion compensating apparatus includes an A/D converter which converts the feedback signal into digital form, an FFT computation unit which computes a spectrum by applying a fast Fourier transform to the output of the A/D converter, a calculation unit which, based on the result of the FFT computation, calculates one of the values of signal-to-noise ratio SNR, adjacent channel leakage power ratio (ACLR), noise level Pn, and valid bit length ENBO, a delay timing determining unit which compares a calculated value at the current time with a calculated value obtained at the immediately preceding time and, based on the result of the comparison, adjusts signal delay time occurring through the distortion device and the feedback loop and determines the delay time by repeating the adjustment, and a delay circuit in which the delay time is set and which adjusts the timing for each of the units of the distortion compensating apparatus.
It is also known to provide an image sensor that includes a plurality of photoelectric conversion devices, a common signal line, a plurality of switching devices inserted between the common signal line and the respective photoelectric conversion devices, and a shift register for sequentially driving these devices. A noise absorbing capacitor, a switching device, and an inverter and capacitor for capacitively coupling a signal has opposite phase compared to a clock signal are connected in series to the common signal line of the image sensor. This serves to reduce the crosstalk noise signal of the clock signal superimposed on the common signal line.
It is also known to provide a distortion compensating apparatus that includes a predistortion unit which applies distortion compensation to an input signal by using a distortion compensating coefficient, a distortion compensating coefficient computing unit which computes a distortion compensating coefficient, based on the input signal before the distortion compensation and on a feedback signal fed back from the output side of the distortion device, and a distortion compensating coefficient storage unit which stores the thus computed distortion compensating coefficient by associating it with the input signal. This distortion compensating apparatus further includes a delay unit which adjusts the amount of delay of the feedback signal by using a digital filter.
It is also known to provide a distortion compensating apparatus that includes a distortion compensating coefficient computing unit which takes as input a difference signal between a transmit signal as a reference signal and a feedback signal, and computes a distortion compensating coefficient by an adaptive algorithm so as to reduce the difference signal, a distortion compensating coefficient storage unit whose stored contents are updated by the thus computed distortion compensating coefficient, and a distortion compensating unit which applies distortion compensation to the transmit signal by using the distortion compensating coefficient. This distortion compensating apparatus further includes a phase difference detection unit which detects a phase difference between the reference signal and the feedback signal, a phase correction unit which corrects the phase difference, and a control unit which generates a phase correction period and a distortion compensating coefficient update period alternately and which performs control so that the phase difference is corrected during the phase correction period and the distortion compensating coefficient is updated during the distortion compensating coefficient update period.
Related art is disclosed in Japanese Laid-open Patent Publication No. 2001-103104, International Publication Pamphlet No. WO2002/087097, Japanese Laid-open Patent Publication No. 06-86006, Japanese Laid-open Patent Publication No. 2001-189685, and International Publication Pamphlet No. WO2003/103163.